The field of the invention relates to communication systems, and in particular, to synchronization for entry to a frequency hopping communication network.
Modern high frequency communication systems commonly utilize frequency hopping spread spectrum waveforms to achieve a high degree of resistance to jamming. To avoid frequency following jammers, the frequency hopping waveform must hop quickly among many frequencies in a pseudo-random fashion. The pseudo-random frequency pattern is conventionally locked to the system timing since frequency hopping is essentially a time-frequency coded technique.
In order to improve resistance to frequency following jammers, the hop rate is made fast enough to prevent a jammer from tracking each hop. This requires transceivers within the network to have very accurate timing with very little time drift between transceiver units. In order for the communication network links to perform properly, all units in the network must have the same timing. The network transceiver must initially synchronize with the rapid frequency hopping code of the network in order to communicate with the network. The transceiver must also maintain accurate timing with low time drift in order to maintain synchronization with the network.
In conventional systems, low power consumption and low cost are often system requirements. These requirements may result in the use of a system time standard that has an initial inaccuracy of tens of seconds and a drift of one or two parts per million. Hence, a synchronization arrangement is needed to initially synchronize a transceiver in the presence of relatively large time errors, and to continually track the synchronization and correct the time to prevent the networked units from drifting apart. Some conventional synchronization techniques use long preambles which allow a receiver to correct its time. Other conventional synchronization techniques use shorter preambles, but still longer than the uncertainty time. However, these techniques use parallel processing of multiple channels.
Accordingly, it is a feature of the present invention to provide a network synchronization arrangement for frequency hopping communication systems that corrects for large initial time errors, and that continuously or periodically updates system timing. Another feature of the invention is the provision of a network synchronization arrangement that does not use long preambles or special broadcasts.